Classics in the History
of Psychology

The Descent of Man (2nd ed.)
Charles Darwin (1874)

PART ONE
DESCENT OR ORIGIN OF MAN

Chapter VI
ON THE AFFINITIES AND GENEALOGY OF MAN.

Even if it be granted that the difference between man and his
nearest allies is as great in corporeal structure as some naturalists
maintain, and although we must grant that the difference between
them is immense in mental power, yet the facts given in the earlier
chapters appear to declare, in the plainest manner, that man is
descended from some lower form, notwithstanding that connecting-links
have not hitherto been discovered.

Man is liable to numerous, slight, and diversified variations,
which are induced by the same general causes, are governed and
transmitted in accordance with the same general laws, as in the
lower animals. Man has multiplied so rapidly, that he has necessarily
been exposed to struggle for existence, and consequently to natural
selection. He has given rise to many races, some of which differ
so much from each other, that they have often been ranked by naturalists
as distinct species. His body is constructed on the same homological
plan as that of other mammals. He passes through the same phases
of embryological development. He retains many rudimentary and
useless structures, which no doubt were once serviceable. Characters
occasionally make their re-appearance in him, which we have reason
to believe were possessed by his early progenitors. If the origin
of man had been wholly different from that of all other animals,
these various appearances would be mere empty deceptions; but
such an admission is incredible. These appearances, on the other
hand, are intelligible, at least to a large extent, if man is
the co-descendant with other mammals of some unknown and lower
form.

Some naturalists, from being deeply impressed with the mental
and spiritual powers of man, have divided the whole organic world
into three kingdoms, the Human, the Animal, and the Vegetable,
thus giving to man a separate kingdom.[323]
Spiritual powers cannot be compared or classed by the naturalist:
but he may endeavour to shew, as I have done, that the mental
faculties of man and the lower animals do not differ in kind,
although immensely in degree. A difference in degree, however
great, does not justify us in placing man in a distinct kingdom,
as will perhaps be best illustrated by comparing the mental powers
of two insects, namely, a coccus or scale-insect and an ant, which
undoubtedly belong to the same class. The difference is here greater
than, though of a somewhat different kind from, that between man
and the highest mammal. The female coccus, whilst young, attaches
itself by its proboscis to a plant; sucks the sap, but never moves
again; is fertilised and lays eggs; and this is its whole history.
On the other hand, to describe the habits and mental powers of
worker-ants, would require, as Pierre Huber has shewn, a large
volume; I may, however, briefly specify a few points. Ants certainly
communicate information to each other, and several unite for the
same work, or for games of play. They recognise their fellow-ants
after months of absence, and feel sympathy for each other. They
build great edifices, keep them clean, close the doors in the
evening, and post sentries. They make roads as well as tunnels
under rivers, and temporary bridges over them, by clinging together.
They collect food for the community, and when an object, too large
for entrance, is brought to the nest, they enlarge the door, and
afterwards build it up again. They store up seeds, of which they
prevent the germination, and which, if damp, are brought up to
the surface to dry. They keep aphides and other insects as milchcows.
They go out to battle in regular bands, and freely sacrifice their
lives for the common weal. They emigrate according to a preconcerted
plan. They capture slaves. They move the eggs of their aphides,
as well as their own eggs and cocoons, into warm parts of the
nest, in order that they may be quickly hatched; and endless similar
facts could be given.[324] On the whole, the
difference in mental power between an ant and a coccus is immense;
yet no one has ever dreamed of placing these insects in distinct
classes, much less in distinct kingdoms. No doubt the difference
is bridged over by other insects; and this is not the case with
man and the higher apes. But we have every reason to believe that
the breaks in the series are simply the results of many forms
having become extinct.

Professor Owen, relying chiefly on the structure of the brain,
has divided the mammalian series into four sub-classes. One of
these he devotes to man; in another he places both the marsupials
and the Monotremata; so that he makes man as distinct from all
other mammals as are these two latter groups conjoined. This view
has not been accepted, as far as I am aware, by any naturalist
capable of forming an independent judgment, and therefore need
not here be further considered.

We can understand why a classification founded on any single character
or organ- even an organ so wonderfully complex and important as
the brain- or on the high development of the mental faculties,
is almost sure to prove unsatisfactory. This principle has indeed
been tried with hymenopterous insects; but when thus classed by
their habits or instincts, the arrangement proved thoroughly artificial.[325]
Classifications may, of course, be based on any character whatever,
as on size, colour, or the element inhabited; but naturalists
have long felt a profound conviction that there is a natural system.
This system, it is now generally admitted, must be, as far as
possible, genealogical in arrangement,- that is, the co-descendants
of the same form must be kept together in one group, apart from
the co-descendants of any other form; but if the parent-forms
are related, so will be their descendants, and the two groups
together will form a larger group. The amount of difference between
the several groups- that is the amount of modification which each
has undergone- is expressed by such terms as genera, families,
orders, and classes. As we have no record of the lines of descent,
the pedigree can be discovered only by observing the degrees of
resemblance between the beings which are to be classed. For this
object numerous points of resemblance are of much more importance
than the amount of similarity or dissimilarity in a few points.
If two languages were found to resemble each other in a multitude
of words and points of construction, they would be universally
recognised as having sprung from a common source, notwithstanding
that they differed greatly in some few words or points of construction.
But with organic beings the points of resemblance must not consist
of adaptations to similar habits of life: two animals may, for
instance, have had their whole frames modified for living in the
water, and yet they will not be brought any nearer to each other
in the natural system. Hence we can see how it is that resemblances
in several unimportant structures, in useless and rudimentary
organs, or not now functionally active, or in an embryological
condition, are by far the most serviceable for classification;
for they can hardly be due to adaptations within a late period;
and thus they reveal the old lines of descent or of true affinity.

We can further see why a great amount of modification in some
one character ought not to lead us to separate widely any two
organisms. A part which already differs much from the same part
in other allied forms has already, according to the theory of
evolution, varied much; consequently it would (as long as the
organism remained exposed to the same exciting conditions) be
liable to further variations of the same kind; and these, if beneficial,
would be preserved, and thus be continually augmented. In many
cases the continued development of a part, for instance, of the
beak of a bird, or of the teeth of a mammal, would not aid the
species in gaining its food, or for any other object; but with
man we can see no definite limit to the continued development
of the brain and mental faculties, as far as advantage is concerned.
Therefore in determining the position of man in the natural or
genealogical system, the extreme development of his brain ought
not to outweigh a multitude of resemblances in other less important
or quite unimportant points.

The greater number of naturalists who have taken into consideration
the whole structure of man, including his mental faculties, have
followed Blumenbach and Cuvier, and have placed man in a separate
Order, under the title of the Bimana, and therefore on an equality
with the orders of the Quadrumana, Carnivora, &c. Recently
many of our best naturalists have recurred to the view first propounded
by Linnaeus, so remarkable for his sagacity, and have placed man
in the same Order with the Quadrumana, under the title of the
primates. The justice of this conclusion will be admitted: for
in the first place, we must bear in mind the comparative insignificance
for classification of the great development of the brain in man,
and that the strongly-marked differences between the skulls of
man and the Quadrumana (lately insisted upon by Bischoff, Aeby,
and others) apparently follow from their differently developed
brains. In the second place, we must remember that nearly all
the other and more important differences between man and the Quadrumana
are manifestly adaptive in their nature, and relate chiefly to
the erect position of man; such as the structure of his hand,
foot, and pelvis, the curvature of his spine, and the position
of his head. The family of seals offers a good illustration of
the small importance of adaptive characters for classification.
These animals differ from all other Carnivora in the form of their
bodies and in the structure of their limbs, far more than does
man from the higher apes; yet in most systems, from that of Cuvier
to the most recent one by Mr. Flower, [326]
seals are ranked as a mere family in the Order of the Carnivora.
If man had not been his own classifier, he would never have thought
of founding a separate order for his own reception.

It would be beyond my limits, and quite beyond my knowledge, even
to name the innumerable points of structure in which man agrees
with the other primates. Our great anatomist and philosopher,
Prof. Huxley, has fully discussed this subject,[327]
and concludes that man in all parts of his organization differs
less from the higher apes, than these do from the lower members
of the same group. Consequently there "is no justification
for placing man in a distinct order."

In an early part of this work I brought forward various facts,
shewing how closely man agrees in constitution with the higher
mammals; and this agreement must depend on our close similarity
in minute structure and chemical composition. I gave, as instances,
our liability to the same diseases, and to the attacks of allied
parasites; our tastes in common for the same stimulants, and the
similar effects produced by them, as well as by various drugs,
and other such facts.

As small unimportant points of resemblance between man and the
Quadrumana are not commonly noticed in systematic works, and as,
when numerous, they clearly reveal our relationship, I will specify
a few such points. The relative position of our features is manifestly
the same; and the various emotions are displayed by nearly similar,
movements of the muscles and skin, chiefly above the eyebrows
and round the mouth. Some few expressions are, indeed, almost
the same, as in the weeping of certain kinds of monkeys and in
the laughing noise made by others, during which the corners of
the mouth are drawn backwards, and the lower eyelids wrinkled.
The external ears are curiously alike. In man the nose is much
more prominent than in most monkeys; but we may trace the commencement
of an aquiline curvature in the nose of the Hoolock gibbon; and
this in the Semnopithecus nasica is carried to a ridiculous extreme.

The faces of many monkeys are ornamented with beards, whiskers,
or moustaches. The hair on the head grows to a great length in
some species of Semnopithecus;[328] and in
the bonnet monkey (Macacus radiatus) it radiates from a point
on the crown, with a parting down the middle. It is commonly said
that the forehead gives to man his noble and intellectual appearance;
but the thick hair on the head of the bonnet monkey terminates
downwards abruptly, and is succeeded by hair so short and fine
that at a little distance the forehead, with the exception of
the eyebrows, appears quite naked. It has been erroneously asserted
that eyebrows are not present in any monkey. In the species just
named the degree of nakedness of the forehead differs in different
individuals; and Eschricht states[329] that
in our children the limit between the hairy scalp and the naked
forehead is sometimes not well defined; so that here we seem to
have a trifling case of reversion to a progenitor, in whom the
forehead had not as yet become quite naked.

It is well known that the hair on our arms tends to converge from
above and below to a point at the elbow. This curious arrangement,
so unlike that in most of the lower mammals, is common to the
gorilla, chimpanzee, orang, some species of Hylobates, and even
to some few American monkeys. But in Hylobates agilis the hair
on the forearm is directed downwards or towards the wrist in the
ordinary manner; and in H. lar it is nearly erect, with only a
very slight forward inclination; so that in this latter species
it is in a transitional state. It can hardly be doubted that with
most mammals the thickness of the hair on the back and its direction,
is adapted to throw off the rain; even the transverse hairs on
the fore-legs of a dog may serve for this end when he is coiled
up asleep. Mr. Wallace, who has carefully studied the habits of
the orang, remarks that the convergence of the hair towards the
elbow on the arms of the orang may be explained as serving to
throw off the rain, for this animal during rainy weather sits
with its arms bent, and with the hands clasped round a branch
or over its head. According to Livingstone, the gorilla also "sits
in pelting rain with his hands over his head."[330]
If the above explanation is correct, as seems probable, the direction
of the hair on our own arms offers a curious record of our former
state; for no one supposes that it is now of any use in throwing
off the rain; nor, in our present erect condition, is it properly
directed for this purpose.

It would, however, be rash to trust too much to the principle
of adaptation in regard to the direction of the hair in man or
his early progenitors; for it is impossible to study the figures
given by Eschricht of the arrangement of the hair on the human
foetus (this being the same as in the adult) and not agree with
this excellent observer that other and more complex causes have
intervened. The points of convergence seem to stand in some relation
to those points in the embryo which are last closed in during
development. There appears, also, to exist some relation between
the arrangement of the hair on the limbs, and the course of the
medullary arteries.[331]

It must not be supposed that the resemblances between man and
certain apes in the above and in many other points- such as in
having a naked forehead, long tresses on the head, &c.,- are
all necessarily the result of unbroken inheritance from a common
progenitor, or of subsequent reversion. Many of these resemblances
are more probably due to analogous variation, which follows, as
I have elsewhere attempted to shew,[332] from
co-descended organisms having a similar constitution, and having
been acted on by like causes inducing similar modifications. With
respect to the similar direction of the hair on the fore-arms
of man and certain monkeys, as this character is common to almost
all the anthropomorphous apes, it may probably be attributed to
inheritance; but this is not certain, as some very distinct American
monkeys are thus characterised.

Although, as we have now seen, man has no just right to form a
separate Order for his own reception, he may perhaps claim a distinct
sub-order or family. Prof. Huxley, in his last work,[333]
divides the primates into three suborders; namely, the Anthropidae
with man alone, the Simiadae including monkeys of all kinds, and
the Lemuridae with the diversified genera of lemurs. As far as
differences in certain important points of structure are concerned,
man may no doubt rightly claim the rank of a sub-order; and this
rank is too low, if we look chiefly to his mental faculties. Nevertheless,
from a genealogical point of view it appears that this rank is
too high, and that man ought to form merely a family, or possibly
even only a sub-family. If we imagine three lines of descent proceeding
from a common stock, it is quite conceivable that two of them
might after the lapse of ages be so slightly changed as still
to remain as species of the same genus, whilst the third line
might become so greatly modified as to deserve to rank as a distinct
sub-family, or even Order. But in this case it is almost certain
that the third line would still retain through inheritance numerous
small points of resemblance with the other two. Here, then, would
occur the difficulty, at present insoluble, how much weight we
ought to assign in our classifications to strongly-marked differences
in some few points,- that is, to the amount of modification undergone;
and how much to close resemblance in numerous unimportant points,
as indicating the lines of descent or genealogy. To attach much
weight to the few but strong differences is the most obvious and
perhaps the safest course, though it appears more correct to pay
great attention to the many small resemblances, as giving a truly
natural classification.

In forming a judgment on this head with reference to man, we must
glance at the classification of the Simiadae. This family is divided
by almost all naturalists into the catarhine group, or Old World
monkeys, all of which are characterised (as their name expresses)
by the peculiar structure of their nostrils, and by having four
premolars in each jaw; and into the platyrhine group or New World
monkeys (including two very distinct sub-groups), all of which
are characterised by differently constructed nostrils, and by
having six premolars in each jaw. Some other small differences
might be mentioned. Now man unquestionably belongs in his dentition,
in the structure of his nostrils, and some other respects, to
the catarhine or Old World division; nor does he resemble the
platyrhines more closely than the catarhines in any characters,
excepting in a few of not much importance and apparently of an
adaptive nature. It is therefore against all probability that
some New World species should have formerly varied and produced
a man-like creature, with all the distinctive characters proper
to the Old World division; losing at the same time all its own
distinctive characters. There can, consequently, hardly be a doubt
that man is an off-shoot from the Old World simian stem; and that
under a genealogical point of view he must be classed with the
catarhine division.[334]

The anthropomorphous apes, namely the gorilla, chimpanzee, orang,
and Hylobates, are by most naturalists separated from the other
Old World monkeys, as a distinct sub-group. I am aware that Gratiolet,
relying on the structure of the brain, does not admit the existence
of this sub-group, and no doubt it is a broken one. Thus the orang,
as Mr. St. G. Mivart remarks, "is one of the most peculiar
and aberrant forms to be found in the Order."[335]
The remaining non-anthropomorphous Old World monkeys, are again
divided by some naturalists into two or three smaller subgroups;
the genus Semnopithecus, with its peculiar sacculated stomach,
being the type of one sub-group. But it appears from M. Gaudry's
wonderful discoveries in Attica, that during the Miocene period
a form existed there, which connected Semnopithecus and Macacus;
and this probably illustrates the manner in which the other and
higher groups were once blended together.

If the anthropomorphous apes be admitted to form a natural sub-group,
then as man agrees with them, not only in all those characters
which he possesses in common with the whole catarhine group, but
in other peculiar characters, such as the absence of a tail and
of callosities, and in general appearance, we may infer that some
ancient member of the anthropomorphous sub-group gave birth to
man. It is not probable that, through the law of analogous variation,
a member of one of the other lower sub-groups should have given
rise to a man-like creature, resembling the higher anthropomorphous
apes in so many respects. No doubt man, in comparison with most
of his allies, has undergone an extraordinary amount of modification,
chiefly in consequence of the great development of his brain and
his erect position; nevertheless, we should bear in mind that
he "is but one of several exceptional forms of primates."[336]

Every naturalist, who believes in the principle of evolution,
will grant that the two main divisions of the Simiadae, namely
the catarhine and platyrhine monkeys, with their sub-groups, have
all proceeded from some one extremely ancient progenitor. The
early descendants of this progenitor, before they had diverged
to any considerable extent from each other, would still have formed
a single natural group; but some of the species or incipient genera
would have already begun to indicate by their diverging characters
the future distinctive marks of the catarhine and platyrhine divisions.
Hence the members of this supposed ancient group would not have
been so uniform in their dentition, or in the structure of their
nostrils, as are the existing catarhine monkeys in one way and
the platyrhines in another way, but would have resembled in this
respect the allied Lemuridae, which differ greatly from each other
in the form of their muzzles,[337] and to
an extraordinary degree in their dentition.

The catarhine and platyrhine monkeys agree in a multitude of characters,
as is shewn by their unquestionably belonging to one and the same
Order. The many characters which they possess in common can hardly
have been independently acquired by so many distinct species;
so that these characters must have been inherited. But a naturalist
would undoubtedly have ranked as an ape or a monkey, an ancient
form which possessed many characters common to the catarhine and
platyrhine monkeys, other characters in an intermediate condition,
and some few, perhaps, distinct from those now found in either
group. And as man from a genealogical point of view belongs to
the catarhine or Old World stock, we must conclude, however much
the conclusion may revolt our pride, that our early progenitors
would have been properly thus designated.[338]
But we must not fall into the error of supposing that the early
progenitors of the whole simian stock, including man, was identical
with, or even closely resembled, any existing ape or monkey.

On the Birthplace and Antiquity of Man.- We are naturally led
to enquire, where was the birthplace of man at that stage of descent
when our progenitors diverged from the catarhine stock? The fact
that they belonged to the stock clearly shews that they inhabited
the Old World; but not Australia nor any oceanic island, as we
may infer from the laws of geographical distribution. In each
great region of the world the living mammals are closely related
to the extinct species of the same region. It is therefore probable
that Africa was formerly inhabited by extinct apes closely allied
to the gorilla and chimpanzee; and as these two species are now
man's nearest allies, it is somewhat more probable that our early
progenitors lived on the African continent than elsewhere. But
it is useless to speculate on this subject; for two or three anthropomorphous
apes, one the Dryopithecus[339] of Lartet,
nearly as large as a man, and closely allied to Hylobates, existed
in Europe during the Miocene age; and since so remote a period
the earth has certainly undergone many great revolutions, and
there has been ample time for migration on the largest scale.

At the period and place, whenever and wherever it was, when man
first lost his hairy covering, he probably inhabited a hot country;
a circumstance favourable for the frugi-ferous diet on which,
judging from analogy, he subsisted. We are far from knowing how
long ago it was when man first diverged from the catarhine stock;
but it may have occurred at an epoch as remote as the Eocene period;
for that the higher apes had diverged from the lower apes as early
as the Upper Miocene period is shewn by the existence of the Dryopithecus.
We are also quite ignorant at how rapid a rate organisms, whether
high or low in the scale, may be modified under favourable circumstances;
we know, however, that some have retained the same form during
an enormous lapse of time. From what we see going on under domestication,
we learn that some of the co-descendants of the same species may
be not at all, some a little, and some greatly changed, all within
the same period. Thus it may have been with man, who has undergone
a great amount of modification in certain characters in comparison
with the higher apes.

The great break in the organic chain between man and his nearest
allies, which cannot be bridged over by any extinct or living
species, has often been advanced as a grave objection to the belief
that man is descended from some lower form; but this objection
will not appear of much weight to those who, from general reasons,
believe in the general principle of evolution. Breaks often occur
in all parts of the series, some being wide, sharp and defined,
others less so in various degrees; as between the orang and its
nearest allies- between the Tarsius and the other Lemuridae- between
the elephant, and in a more striking manner between the Ornithorhynchus
or Echidna, and all other mammals. But these breaks depend merely
on the number of related forms which have become extinct. At some
future period, not very distant as measured by centuries, the
civilised races of man will almost certainly exterminate, and
replace, the savage races throughout the world. At the same time
the anthropomorphous apes, as Professor Schaaffhausen has remarked,[340]
will no doubt be exterminated. The break between man and his nearest
allies will then be wider, for it will intervene between man in
a more civilised state, as we may hope, even than the Caucasian,
and some ape as low as a baboon, instead of as now between the
negro or Australian and the gorilla.

With respect to the absence of fossil remains, serving to connect
man with his ape-like progenitors, no one will lay much stress
on this fact who reads Sir C. Lyell's discussion,[341]
where he shews that in all the vertebrate classes the discovery
of fossil remains has been a very slow and fortuitous process.
Nor should it be forgotten that those regions which are the most
likely to afford remains connecting man with some extinct ape-like
creature, have not as yet been searched by geologists.

Lower Stages in the Genealogy of Man.- We have seen that man appears
to have diverged from the catarhine or Old World division of the
Simiadae, after these had diverged from the New World division.
We will now endeavour to follow the remote traces of his genealogy,
trusting principally to the mutual affinities between the various
classes and orders, with some slight reference to the periods,
as far as ascertained, of their successive appearance on the earth.
The Lemuridae stand below and near to the Simiadae, and constitute
a very distinct family of the primates, or, according to Haeckel
and others, a distinct Order. This group is diversified and broken
to an extraordinary degree, and includes many aberrant forms.
It has, therefore, probably suffered much extinction. Most of
the remnants survive on islands, such as Madagascar and the Malayan
archipelago, where they have not been exposed to so severe a competition
as they would have been on well-stocked continents. This group
likewise presents many gradations, leading, as Huxley remarks,[342]
"insensibly from the crown and summit of the animal creation
down to creatures from which there is but a step, as it seems,
to the lowest, smallest, and least intelligent of the placental
mammalia." From these various considerations it is probable
that the Simiadae were originally developed from the progenitors
of the existing Lemuridae; and these in their turn from forms
standing very low in the mammalian series.

The marsupials stand in many important characters below the placental
mammals. They appeared at an earlier geological period, and their
range was formerly much more extensive than at present. Hence
the Placentata are generally supposed to have been derived from
the Implacentata or marsupials; not, however, from forms closely
resembling the existing marsupials, but from their early progenitors.
The Monotremata are plainly allied to the marsupials, forming
a third and still lower division in the great mammalian series.
They are represented at the present day solely by the Ornithorhynchus
and Echidna; and these two forms may be safely considered as relics
of a much larger group, representatives of which have been preserved
in Australia through some favourable concurrence of circumstances.
The Monotremata are eminently interesting, as leading in several
important points of structure towards the class of reptiles.

In attempting to trace the genealogy of the Mammalia, and therefore
of man, lower down in the series, we become involved in greater
and greater obscurity; but as a most capable judge, Mr. Parker,
has remarked, we have good reason to believe, that no true bird
or reptile intervenes in the direct line of descent. He who wishes
to see what ingenuity and knowledge can effect, may consult Prof.
Haeckel's works.[343] I will content myself
with a few general remarks. Every evolutionist will admit that
the five great vertebrate classes, namely, mammals, birds, reptiles,
amphibians, and fishes, are descended from some one prototype;
for they have much in common, especially during their embryonic
state. As the class of fishes is the most lowly organised, and
appeared before the others, we may conclude that all the members
of the vertebrate kingdom are derived from some fishlike animal.
The belief that animals so distinct as a monkey, an elephant,
a humming-bird, a snake, a frog, and a fish, &c., could all
have sprung from the same parents, will appear monstrous to those
who have not attended to the recent progress of natural history.
For this belief implies the former existence of links binding
closely together all these forms, now so utterly unlike.

Nevertheless, it is certain that groups of animals have existed,
or do now exist, which serve to connect several of the great vertebrate
classes more or less closely. We have seen that the Ornithorhynchus
graduates towards reptiles; and Prof. Huxley has discovered, and
is confirmed by Mr. Cope and others, that the dinosaurians are
in many important characters intermediate between certain reptiles
and certain birds- the birds referred to being the ostrich-tribe
(itself a widelydiffused remnant of a larger group) and the Archeopteryx,
that strange secondary bird, with a long lizard-like tail. Again,
according to Prof. Owen, [344] the ichthyosaurians
- great sea-lizards furnished with paddles - present many affinities
with fishes, or rather, according to Huxley, with amphibians;
a class which, including in its highest division frogs and toads,
is plainly allied to the ganoid fishes. These latter fishes swarmed
during the earlier geological periods, and were constructed on
what is called a generalised type, that is, they presented diversified
affinities with other groups of organisms. The Lepidosiren is
also so closely allied to amphibians and fishes, that naturalists
long disputed in which of these two classes to rank it; it, and
also some few ganoid fishes, have been preserved from utter extinction
by inhabiting rivers, which are harbours of refuge, and are related
to the great waters of the ocean in the same way that islands
are to continents.

Lastly, one single member of the immense and diversified class
of fishes, namely, the lancelet or amphioxus, is so different
from all other fishes, that Haeckel maintains that it ought to
form a distinct class in the vertebrate kingdom. This fish is
remarkable for its negative characters; it can hardly be said
to possess a brain, vertebral column, or heart, &c.; so that
it was classed by the older naturalists amongst the worms. Many
years ago Prof. Good sir perceived that the lancelet presented
some affinities with the ascidians, which are invertebrate, hermaphrodite,
marine creatures permanently attached to a support. They hardly
appear like animals, and consist of a simple, tough, leathery
sack, with two small projecting orifices. They belong to the Mulluscoida
of Huxley- a lower division of the great kingdom of the Mollusca;
but they have recently been placed by some naturalists amongst
the Vermes or worms. Their larvae somewhat resemble tadpoles in
shape,[345] and have the power of swimming
freely about. Mr. Kovalevsky[346] has lately
observed that the larvae of ascidians are related to the Vertebrata,
in their manner of development, in the relative position of the
nervous system, and in possessing a structure closely like the
chorda dorsalis of vertebrate animals; and in this he has been
since confirmed by Prof. Kupffer. M. Kovalevsky writes to me from
Naples, that he has now carried these observations yet further,
and should his results be well established, the whole will form
a discovery of the very greatest value. Thus, if we may rely on
embryology, ever safest guide in classification, it seems that
we have at last gained a clue to the source whence the Vertebrata
were derived.[347] We should then be justified
in believing that at an extremely remote period a group of animals
existed, resembling in many respects the larvae of our present
ascidians, which diverged into two great branches- the one retrograding
in development and producing the present class of ascidians, the
other rising to the crown and summit of the animal kingdom by
giving birth to the Vertebrata.

We have thus far endeavoured rudely to trace the genealogy of
the Vertebrata by the aid of their mutual affinities. We will
now look to man as he exists; and we shall, I think, be able partially
to restore the structure of our early progenitors, during successive
periods, but not in due order of time. This, can be effected by
means of the rudiments which man still retains, by the characters
which occasionally make their appearance in him through reversion,
and by the aid of the principles of morphology and embryology.
The various facts, to which I shall here allude, have been given
in the previous chapters.

The early progenitors of man must have been once covered with
hair, both sexes having beards; their ears were probably pointed,
and capable of movement; and their bodies were provided with a
tail, having the proper muscles. Their limbs and bodies were also
acted on by many muscles which now only occasionally reappear,
but are normally present in the Quadrumana. At this or some earlier
period, the great artery and nerve of the humerus ran through
a supra-condyloid foramen. The intestine gave forth a much larger
diverticulum or caecum than that now existing. The foot was then
prehensile, judging from the condition of the great toe in the
foetus; and our progenitors, no doubt, were arboreal in their
habits, and frequented some warm, forest-clad land. The males
had great canine teeth, which served them as formidable weapons.
At a much earlier period the uterus was double; the excreta were
voided through a cloaca; and the eye was protected by a third
eyelid or nictitating membrane. At a still earlier period the
progenitors of man must have been aquatic in their habits; for
morphology plainly tells us that our lungs consist of a modified
swimbladder, which once served as a float. The clefts on the neck
in the embryo of man show where the branchiae once existed. In
the lunar or weekly recurrent periods of some of our functions
we apparently still retain traces of our primordial birthplace,
a shore washed by the tides. At about this same early period the
true kidneys were replaced by the corpora wolffiana. The heart
existed as a simple pulsating vessel; and the chorda dorsalis
took the place of a vertebral column. These early ancestors of
man, thus seen in the dim recesses of time, must have been as
simply, or even still more simply organised than the lancelet
or amphioxus.

There is one other point deserving a fuller notice. It has long
been known that in the vertebrate kingdom one sex bears rudiments
of various accessory parts, appertaining to the reproductive system,
which properly belong to the opposite sex; and it has now been
ascertained that at a very early embryonic period both sexes possess
true male and female glands. Hence some remote progenitor of the
whole vertebrate kingdom appears to have been hermaphrodite or
androgynous.[348] But here we encounter a
singular difficulty. In the mammalian class the males possess
rudiments of a uterus with the adjacent passage, in their vesiculae
prostaticae; they bear also rudiments of mammae, and some male
marsupials have traces of a marsupial sack.[349]
Other analogous facts could be added. Are we, then, to suppose
that some extremely ancient mammal continued androgynous, after
it had acquired the chief distinctions of its class, and therefore
after it had diverged from the lower classes of the vertebrate
kingdom? This seems very improbable, for we have to look to fishes,
the lowest of all the classes, to find any still existent androgynous
forms.[350] That various accessory parts,
proper to each sex, are found in a rudimentary condition in the
opposite sex, may be explained by such organs having been gradually
acquired by the one sex, and then transmitted in a more or less
imperfect state to the other. When we treat of sexual selection,
we shall meet with innumerable instances of this form of transmission,-
as in the case of the spurs, plumes, and brilliant colours, acquired
for battle or ornament by male birds, and inherited by the females
in an imperfect or rudimentary condition.

The possession by male mammals of functionally imperfect mammary
organs is, in some respects, especially curious. The Monotremata
have the proper milksecreting glands with orifices, but no nipples;
and as these animals stand at the very base of the mammalian series,
it is probable that the progenitors of the class also had milk-secreting
glands, but no nipples. This conclusion is supported by what is
known of their manner of development; for Professor Turner informs
me, on the authority of Kolliker and Langer, that in the embryo
the mammary glands can be distinctly traced before the nipples
are in the least visible; and the development of successive parts
in the individual generally represents and accords with the development
of successive beings in the same line of descent. The marsupials
differ from the Monotremata by possessing nipples; so that probably
these organs were first acquired by the marsupials, after they
had diverged from, and risen above, the Monotremata, and were
then transmitted to the placental mammals.[351]
No one will suppose that the marsupials still remained androgynous,
after they had approximately acquired their present structure.
How then are we to account for male mammals possessing mammae?
It is possible that they were first developed in the females and
then transferred to the males, but from what follows this is hardly
probable. It may be suggested, as another view, that long after
the progenitors of the whole mammalian class had ceased to be
androgynous, both sexes yielded milk, and thus nourished their
young; and in the case of the marsupials, that both sexes carried
their young in marsupial sacks. This will not appear altogether
improbable, if we reflect that the males of existing syngnathous
fishes receive the eggs of the females in their abdominal pouches,
hatch them, and afterwards, as some believe, nourish the young;-[352]
that certain other male fishes hatch the eggs within their mouths
or branchial cavities;- that certain male toads take the chaplets
of eggs from the females, and wind them round their own thighs,
keeping them there until the tadpoles are born;- that certain
male birds undertake the whole duty of incubation, and that male
pigeons, as well as the females, feed their nestlings with a secretion
from their crops. But the above suggestion first occurred to me
from mammary glands of male mammals being so much more perfectly
developed than the rudiments of the other accessory reproductive
parts, which are found in the one sex though proper to the other.
The mammary glands and nipples, as they exist in male mammals,
can indeed hardly be called rudimentary; they are merely not fully
developed, and not functionally active. They are sympathetically
affected under the influence of certain diseases, like the same
organs in the female. They often secrete a few drops of milk at
birth and at puberty: this latter fact occurred in the curious
case before referred to, where a young man possessed two pairs
of mammee. In man and some other male mammals these organs have
been known occasionally to become so well developed during maturity
as to yield a fair supply of milk. Now if we suppose that during
a former prolonged period male mammals aided the females in nursing
their offspring,[353] and that afterwards
from some cause (as from the production of a smaller number of
young) the males ceased to give this aid, disuse of the organs
during maturity would lead to their becoming inactive; and from
two well-known principles of inheritance, this state of inactivity
would probably be transmitted to the males at the corresponding
age of maturity. But at an earlier age these organs would be left
unaffected, so that they would be almost equally well developed
in the young of both sexes.

Conclusion.- Von Baer has defined advancement or progress in the
organic scale better than any one else, as resting on the amount
of differentiation and specialisation of the several parts of
a being,- when arrived at maturity, as I should be inclined to
add. Now as organisms have become slowly adapted to diversified
lines of life by means of natural selection, their parts will
have become more and more differentiated and specialised for various
functions from the advantage gained by the division of physiological
labour. The same part appears often to have been modified first
for one purpose, and then long afterwards for some other and quite
distinct purpose; and thus all the parts are rendered more and
more complex. But each organism still retains the general type
of structure of the progenitor from which it was aboriginally
derived. In accordance with this view it seems, if we turn to
geological evidence, that organisation on the whole has advanced
throughout the world by slow and interrupted steps. In the great
kingdom of the Vertebrata it has culminated in man. It must not,
however, be supposed that groups of organic beings are always
supplanted, and disappear as soon as they have given birth to
other and more perfect groups. The latter, though victorious over
their predecessors, may not have become better adapted for all
places in the economy of nature. Some old forms appear to have
survived from inhabiting protected sites, where they have not
been exposed to very severe competition; and these often aid us
in constructing our genealogies, by giving us a fair idea of former
and lost populations. But we must not fall into the error of looking
at the existing members of any lowly-organised group as perfect
representatives of their ancient predecessors.

The most ancient progenitors in the kingdom of the Vertebrata,
at which we are able to obtain an obscure glance, apparently consisted
of a group of marine animals,[354] resembling
the larvae of existing ascidians. These animals probably gave
rise to a group of fishes, as lowly organised as the lancelet;
and from these the ganoids, and other fishes like the Lepidosiren,
must have been developed. From such fish a very small advance
would carry us on to the amphibians. We have seen that birds and
reptiles were once intimately connected together; and the Monotremata
now connect mammals with reptiles in a slight degree. But no one
can at present say by what line of descent the three higher and
related classes, namely, mammals, birds, and reptiles, were derived
from the two lower vertebrate classes, namely, amphibians and
fishes. In the class of mammals the steps are not difficult to
conceive which led from the ancient Monotremata to the ancient
marsupials; and from these to the early progenitors of the placental
mammals. We may thus ascend to the Lemuridae; and the interval
is not very wide from these to the Simiadae. The Simiadae then
branched off into two great stems, the New World and Old World
monkeys; and from the latter, at a remote period, Man, the wonder
and glory of the Universe, proceeded.

Thus we have given to man a pedigree of prodigious length, but
not, it may be said, of noble quality. The world, it has often
been remarked, appears as if it had long been preparing for the
advent of man: and this, in one sense is strictly true, for he
owes his birth to a long line of progenitors. If any single link
in this chain had never existed, man would not have been exactly
what he now is. Unless we wilfully close our eyes, we may, with
our present knowledge, approximately recognise our parentage;
nor need we feel ashamed of it. The most humble organism is something
much higher than the inorganic dust under our feet; and no one
with an unbiased mind can study any living creature, however humble,
without being struck with enthusiasm at its marvellous structure
and properties.

[352] Mr. Lockwood believes (as quoted in Quart. Journal of Science,
April, 1868, p. 269), from what he has observed of the development
of Hippocampus, that the walls of the abdominal pouch of the male
in some way afford nourishment. On male fishes hatching the ova
in their mouths, see a very interesting paper by Prof. Wyman,
in Proc. Boston Soc. of Nat. Hist., Sept. 15, 1857; also Prof.
Turner, in Journal of Anatomy and Physiology, Nov. 1, 1866, p.
78. Dr. Gunther has likewise described similar cases